1. Field of the Invention
The present invention relates to a radiotherapy apparatus suited to performing, e.g., radiotherapy on a tumor by a stereotactic pluridirectional irradiation method.
2. Description of the Related Art
A stereotactic pluridirectional irradiation method is one radiotherapy method capable of increasing the therapeutic effect by intensively irradiating a diseased part with radiation in multiple directions, and minimizing the exposure dose of the surrounding tissue of the diseased part.
This stereotactic pluridirectional irradiation method is considered effective in curing diseased parts, such as a primary benign brain tumor, a simple metastatic brain tumor having a size of 3 cm or less, a small morbid part in the brain, e.g., skull base metastasis which is difficult to operate, arterial malformation, and venous malformation.
As a radiotherapy apparatus capable of practicing this stereotactic pluridirectional irradiation method, an apparatus which performs irradiation after positioning an irradiation head with respect to a patient by using a positioning means is conventionally known. Since, however, a doctor or assistant does not confirm the position of a focus by directly viewing the irradiation field before irradiation, the accuracy of irradiation is not high.
International Patent Laid-Open Nos. 6-502330 and 8-504347 disclose a system which combines a radiotherapy apparatus with an X-ray CT apparatus by incorporating a linear accelerator into a rotary drum of the X-ray CT apparatus. In this system, irradiation can be performed while confirming an image of the irradiation field.
Unfortunately, these apparatuses have a structure in which the linear accelerator is incorporated into the rotary drum of the X-ray CT apparatus. Therefore, irradiation can be performed only around one rotational axis, thus this irradiation is limited to isocentric irradiation.